Outlays Expected to Jump 83% This Year, but Remain Small Compared to Time on Devices

After less than a decade of existence, smartphones and tablets this year will draw more money from advertisers than the centuries-old newspaper industry or the nearly century-old radio sector, a sign of just how rapidly technology is transforming media habits.

But given how much time Americans spend on their devices, mobile-ad spending could be much higher, an indication that marketers remain uncertain about the medium's...